Energy storage system with pressurized support and method thereof

ABSTRACT

Apparatus for heat storage, comprises a working fluid chamber for storing working fluid; a pressure support chamber coupled to the working fluid chamber and including pressure support material, said pressure support chamber for increasing pressure in said working fluid chamber responsive to compression of said pressure support chamber; a fluid pump for pumping working fluid into the working fluid chamber, wherein pumping fluid into the working fluid chamber increases pressure of said working fluid in the working fluid chamber; the pressure elevation of the working fluid in the fluid chamber is responsive to pumping the fluid back into the fluid chamber to compress the pressure support chamber; a working fluid chamber heat exchanger for varying temperature in said working fluid chamber; an output conduit for transferring working fluid from said fluid chamber to a utilization destination; and an input conduit for transferring said working fluid received from said utilization destination to said working fluid into the fluid chamber.

CROSS-REFERENCE TO RELATED APPLICATIONS

This non-provisional application claims the benefit under 35 U.S.C. § 119(e) of U.S. Application Ser. No. 62/781,950 filed on Dec. 19, 2018 entitled “Enthalpy Storage System Based On Piston Connected Pressurized Vessels”, and whose entire disclosure is incorporated by reference herein.

FIELD OF THE INVENTION

The present invention relates to energy storage and in particular to heat storage. Specifically, a method and apparatus are disclosed for heat storage in combination with a pneumatic system in order to obtain high energy density.

BACKGROUND OF THE INVENTION

With the continuous cost decline of solar and wind technologies, renewable power is becoming an increasingly competitive alternative to fossil-fuel based power (IRENA, 2018, Renewable Power Generation Costs in 2017, International Renewable Energy Agency, Abu Dhabi).

The increase in renewable power generation will allow effective carbon emissions reduction in key segments of the energy market. The electricity sector is undergoing a period of rapid change in the scale and breadth of renewable power generation technologies. At the end of 2016, total renewable power generation capacity surpassed 2000 GW, double the capacity of 2012 in a time window of 5 years.

In order for renewable power generation to grow to substantial levels, electricity systems will require great flexibility. This means electricity will need to be stored over days, weeks or months. Thus, energy storage will play a vital role in transforming the energy sector to high level shares of variable renewable generations in the near future. Bloomberg NEF (BNEF) estimates that the global energy storage market will grow to a cumulative 942GW/2857GWh by 2040, attracting $620 billion in investment over the next 22 years. This conclusion is consistent with the conclusion reached in the Electrification Future Study (EFS) (Hale, Elaine, Henry Horsey, Brandon Johnson, Matteo Muratori, Eric Wilson, et al. 2018. The Demand-side Grid (dsgrid) Model Documentation. Golden, Colo.: National Renewable Energy Laboratory. NREL/TP-6A20-71492).

Batteries are currently an active research direction for energy storage due to their many advantages, including high energy density and fast response. The main disadvantage of batteries, however, is short lifetime. Looking into the future, battery recycling may become a huge burden, which is an issue that is typically not included in the cost analysis.

Under the big picture of the Electrification Future Study (EFS) and the forecasted tremendous need for energy storage, heat and cold storage may also account for a large percentage of future energy storage. First, it is reported that HVAC accounts for 35% of total primary energy in the United States, and is expected to reach similar proportions in other countries (Michael Waite, Elliot Cohen, Henri Torbey, Michael Piccirilli, Yu Tian, Vijay Modi. Global trends in urban electricity demands for cooling and heating. Energy 2017: (127): 786-802). This means heat and cold storage can share a large proportion of the total energy storage market, even though the supply is currently dominated by fossil fuels, such as coal and gas. There is significant potential to upgrade existing systems and create new networks that are based on renewable energy sources, in which thermal storage will play a vital role. Second, it cheaper to store the electricity in the form of heat and cold energy for direct heating and cooling applications than to use battery storage. Third, the literature reports that the dynamical load control of refrigerators in a network achieves a significant delay in frequency-fall, thus reducing dependence on rapidly deployable backup generations (Joe A. Short, David G. Infield, and Leon L. Freries, Stabilization of grid frequency through dynamic demand control. IEEE transactions on power systems, 22(3):1284-1293, 2007).

This means HVAC systems with thermal storage capacity have great potential to be used as demand-side load management units for grid frequency stabilization. This may be of vital importance under the scenario of the large sharing of renewable power generation.

Energy storage is known in the art. See U.S. 2014/0109561, U.S. Pat. Nos. 7,832,207, and 9,482,109 each of which is incorporated by reference in its entirety.

SUMMARY OF THE INVENTION

Apparatus for heat storage, comprises a working fluid chamber for storing working fluid; a pressure support chamber coupled to the working fluid chamber and including pressure support material, said pressure support chamber for increasing pressure in said working fluid chamber responsive to compression of said pressure support chamber; a fluid pump for pumping working fluid into the working fluid chamber, wherein pumping fluid into the working fluid chamber increases pressure of said working fluid in the working fluid chamber; the pressure elevation of the working fluid in the fluid chamber is responsive to pumping the fluid back into the fluid chamber to compress the pressure support chamber; a working fluid chamber heat exchanger for varying temperature in said working fluid chamber; an output conduit for transferring working fluid from said fluid chamber to a utilization destination; and an input conduit for transferring said working fluid received from said utilization destination to said working fluid into the fluid chamber.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram that illustrates a heat storage apparatus in accordance with a first exemplary embodiment of the present invention.

FIG. 2 is a block diagram of a common vessel with piston connected chambers in accordance with an exemplary embodiment of the present invention.

FIG. 3 is a diagram that illustrates an exemplary thermal cycle of refrigerant.

FIG. 4 is a block diagram that illustrates an exemplary apparatus that provides a pressure supplement for constant pressure discharge control.

FIG. 5 is a block diagram that illustrates an exemplary enforces piston structure.

FIG. 6 is a block diagram that illustrates an exemplary configuration of two vessels with a common piston connection.

FIG. 7A is a block diagram that illustrates an exemplary energy storage apparatus for domestic steam heating.

FIG. 7B is a block diagram that illustrates how some of the concepts illustrated in FIG. 7A may be integrated

FIG. 8 is a block diagram that illustrates an exemplary mixer for producing saturated steam.

FIG. 9 is a graph that illustrates exemplary annual heat consumption per unit floor area with different insulation levels.

FIG. 10 is a block diagram that illustrates an exemplary enthalpy storage apparatus for fast ramping service for the grid.

DETAILED DESCRIPTION

FIG. 1 is a block diagram of an exemplary embodiment of the present invention that is suitable for energy storage and utilization. The storage medium is a working fluid that being stored in a chamber within a vessel whose pressure is being boosted by a gas chamber in the same vessel. The working fluid and the gas can also be stored in separated vessels with piston connections for pressure support and management. For simplicity, all the illustrations are based on chambers in a same vessel.

More specifically, FIG. 1 illustrates heat storage apparatus 100. Vessel 15 is an exemplary storage apparatus that is separated into two parts, namely working fluid chamber 10 and pressure support chamber 20. In this embodiment, working fluid chamber 10 and pressure support chamber 20 are separated by piston 30 that inversely affects the volume of working fluid chamber 10 and pressure support chamber 20. Thus, as piston 30 moves, different effects are achieved. As the volume of working fluid chamber 10 increases the volume of pressure support chamber 20 decreases, and vice versa. Piston 30 creates a tight seal with the inner walls of vessel 15, and may be supported with appropriate tracks, guides, shafts, etc, so that piston 30 is able to slide within vessel 15. In this manner, piston 30 seals and separates working fluid chamber 10 and pressure support chamber 20 by forming a barrier therebetween. Alternatively, working fluid chamber 10 and pressure support chamber 20 are located in respectively different containers with a piston apparatus therebetween (described and illustrated below), so that pressure in working fluid chamber 10 changes responsive to volumetric change of pressure support chamber 20.

Vessel 15 can be formed in any shape, although a cylindrical shape is preferred for its inherent strength. The walls of vessel 15 may be formed of any material or thickness sufficient to contain the pressure levels generated within, although steel is preferred. The use of one or more layers of high tensile strength steel wire (or other materials such as carbon fiber) may be included as appropriate to further prevent sidewall rupture. End caps may optionally be reinforced with high-tensile rods. The interior of vessel 15 may have various linings (metal, ceramic, polymer, etc) to further prevent leakage. Vessel 15 may also be insulated.

Vessel 15 may be constructed with various safety features, including “leak before burst,” safety (or relief) valves, etc.

Working fluid chamber 10 is filled with a working fluid, e.g. a fluid such as water, and the fluid may be in a gas state, or a combination gas/liquid state. The temperature of the fluid is increased via second heat exchanger 80. Thus, this exchanger 80 (a working fluid chamber heat exchanger) is for varying temperature in said working fluid chamber. The heated fluid passes through valve 115 and travels via vapor conduit 90 (e.g. output conduit) as overheated vapor. The overheated vapor enters heat and work utilization units 18 where it is used for heating and/or energy production (i.e. a steam powered turbine).

Pressure support chamber 20 defines a void and may optionally include an elastic container that is comprises of elastic material. The elastic container may be, for example, a balloon or a tire that may be sealed and that encapsulates the void. Pressure support chamber may be filled (within optional elastic container if present) with pressure support material such as gas and/or liquid. In an exemplary embodiment, a refrigerant is included in pressure support chamber 20. Exemplary refrigerants include R134a, R422B, R414B and so on.

The pressure within the pressure support chamber can be managed through heating/cooling and/or pumping (via piston 30). Thus, first heat exchanger 60 is optionally included for changing the internal temperature of pressure support material in pressure support chamber 20. Thus, this heat exchanger may increase pressure in pressure support chamber 20 by heating the pressure support material. First heat exchanger 60 may receive heat charging via first heat charging source 40, cooling via cooling source 50 (a further cooling source) and/or further cooling via cooling conduit 65 (explained further below). Valves 115 are included for regulating flow of liquids for heating and/or cooling. Pump 95 is also included for regulating flow of liquid via cooling conduit 65.

After fluid releases heat energy within heat and work utilization units 18, cooled fluid exits units 18 and is collected within working fluid reservoir 35. An optional conduit allows fluid within working fluid reservoir 35 to be mixed with overheated vapor within vapor conduit 90 and reintroduced into heat and work utilization units 18. Thus, optional valve 115 is included for regulating flow of liquid between working fluid reservoir 35 and vapor conduit 90.

As working fluid chamber 10 needs to be refilled, a fluid transferor such as pump 95 and/or valve 115 is actuated to allow fluid to flow from working fluid reservoir 35 to working fluid chamber 10 via conduit 25. Thus, a fluid transferor transfers working fluid into working fluid chamber 10. Transferring fluid into working fluid chamber 10 increases pressure of the working fluid in the working fluid chamber. The pressure elevation of the working fluid in working fluid chamber 10 is responsive to transferring the fluid back into fluid chamber 10 to compress pressure support chamber 20. In some exemplary embodiments, conduit 25 allows first heat exchanger 60 to be bypassed.

Working fluid chamber 10 is intended to store temperature energy, while pressure support chamber 20 is intended to store pressure energy. In an exemplary embodiment of the present invention, when the working fluid in working fluid chamber 10 is pressurized at a high pressure level, the working fluid can be heated to a high temperature without concern of evaporation. Thus, a large temperature gradient of a working liquid can be obtained for sensible energy storage, which means high heat density. With the stored energy in the form of both pressure and temperature, this process can be referred to as enthalpy storage.

When the pressurized high temperature working fluid is released to a lower pressure environment (for example within heat and work utilization units 18), the working fluid is transformed from a liquid state to a gas state and the heat energy is carried by a vapor flow with high speed. This results in a high heat transfer rate and fast dynamical response, a feature lacking from other currently available methods of energy storage (such as molten salt, hot rocks or concrete, and PCMs).

The high energy density feature can be illustrated by the application of producing steam for space heating. A traditional water tank can only store hot water under 100° C., so its application is very limited. In an exemplary embodiment of the present invention, with water as the working fluid, water can be stored at a temperature much higher than 100° C. when it is under high pressure. When the water is released to an atmosphere environment, it becomes overheated vapor, and the vapor can be further used to vaporize more liquid water to produce low temperature steam for space heating (for example for a single house, a building or a district).

FIG. 2 shows exemplary single vessel 15 with piston 30 that is connecting chambers 10,20. This exemplary embodiment provides pressure management for heat storage apparatus 100. Thus, pressure support chamber 20 increases pressure in working fluid chamber 10 responsive to compression of the pressure support chamber 20. A single pressurized vessel with piston connected chambers can be referred to as an enthalpy storage vessel. As previously explained, elastic container 37 may be encapsulated within chamber 20 and may be comprised of structure such as a balloon or a tire for enforced sealing or corrosion protection purposes. Based on the actual application, single vessel 15 may be replaced with two separated vessels (as explained below).

In one exemplary embodiment, pressure support chamber 20 for pressure support can just contain gas. In a further exemplary embodiment, first heat exchanger 60 is optional, as the enclosed gas can be compressed by pumping the working fluid from a reservoir back into the working fluid chamber 10, thus create high pressure for the working fluid in working fluid chamber 10. Pumping liquid is of higher efficiency than compressing gas directly, so it is a cost effective operation. The pressure of the gas in the pressure support chamber 20 can be further elevated through heating according to thermodynamic law.

To reduce or in some embodiments eliminate the use of pumping energy, one approach is the use of a suitable refrigerant or chemical substance in the gas chamber that can go through phase changes as a result of heating or cooling. To increase overall energy efficiency of heat storage apparatus 100, in one exemplary embodiment, working fluid may be stored in working fluid reservoir 35 after releasing energy in heat and work utilization units 18. When the working fluid is then pumped back into working fluid chamber 10 from reservoir 35, the working fluid first goes through heat exchanger unit 60, so that refrigerant, which may be selected based on the application temperature range, is cooled and is expected to change from gas to liquid. This results in pressure reduction in the pressure support chamber 20. In this manner, less pumping energy may be required to pump the working fluid back into pressure support chamber 20.

Thus, the working fluid received from units 18 is used to cool the pressure support material in the pressure support chamber via heat exchanger unit 60. The pressure in working fluid chamber 10 decreases responsive to the pressure support material in pressure support chamber 20 being cooled.

After cooling of the refrigerant, if the pressure in working fluid chamber 10 becomes lower than that in the reservoir, then the pump (and associated pumping energy) could be eliminated. Thus, the selection of refrigerant and/or potential chemical substance is performed to achieve a desirable pressure management purpose.

The above steps may be performed under microprocessor control. To summarize, in one exemplary embodiment of the present invention, the following steps may be performed:

-   -   1) Heating the pressure support material via heat exchanger 60         to transition the pressure support material from liquid to gas         and increase the pressure in the pressure support chamber 20;     -   2) Opening valve 115 to allow the working fluid to exit the         working fluid chamber 10 and interact with the utilization units         18;     -   3) Allowing the working fluid to cool the pressure support         material after interacting with the utilization units 18; and     -   4) Refilling the working fluid into the working fluid chamber 10         after interacting with the utilization units.

In more detail, FIG. 3 shows an example of a thermal cycle of pressure support chamber 20, when it is filled with a refrigerant. During the heat charging process (Stage 1), the refrigerant turns from liquid to gas and is further heated to further increase the pressure in working fluid chamber 10 (via compression). Note that the pressure in working fluid chamber 10 is already elevated during the stage of pumping the working fluid back to working fluid chamber 10. The working fluid in working fluid chamber 10 is also heated to achieve a higher temperature gradient for heat storage. The heat sources can be solar, thermal, waste heat, electric heaters and so on. During the heat releasing stage (Stage 2), with an opening valve, the hot working fluid is gradually pushed out of working fluid chamber 10 in a controlled manner by expansion of the refrigerant in pressure support chamber 20 due to a lower pressure environment outside. Based on the pressures, the working fluid could turn into overheated vapor and provide heat for applications. The high temperature and high pressure vapor can also be used to turn a turbine to generate electricity. After utilization, the working fluid is recycled in reservoir 35. At stages 3 and 4, the working fluid is pumped back to the working fluid chamber 10. First it is used as a cooling source to cool the refrigerant in pressure support chamber 20 (Stage 3), turning it from gas to liquid to reduce the pressure in the working fluid chamber 10. An extra cooling source could be considered based on whether it is economical to achieve overall higher system efficiency. When the pressure being created in the working fluid chamber 10 through cooling is lower than the pressure in reservoir 35, pumping energy for the working fluid may be eliminated. The refrigerant cooling and working fluid refilling (Stages 3 and 4) take place simultaneously. With a refilled working fluid chamber 10, heat storage apparatus 100 is ready for heat charging and begins a new cycle.

With the discharge of the working fluid from working fluid chamber 10, the pressure energy in the system decreases and thus causes a continuous drop of the output pressure. If the final discharge pressure is greater than the saturation pressure of the working fluid being stored, the working fluid in working fluid chamber 10 will not vaporize and its temperature will remain at its initial stored point. Otherwise, partial working fluid will vaporize in working fluid chamber 10 to maintain working fluid chamber 10 at a saturation pressure that matches the temperature of the working fluid inside it. Usually, partial evaporation inside working fluid chamber 10 will not adversely impact operation of heat storage apparatus 100, but the temperature of the stored working fluid will experience some decrease due to the heat energy being used for evaporation. Whether this temperature drop is substantial and consequently falls short to meet the heat requirement by the application depends on the outlet pressure range between the initial and final states, as well as the initial temperature of the working fluid being stored.

Aiming to address the above issue, and also to bring out other operational benefits, an exemplary embodiment of the present invention relates to a strategy to realize constant pressure discharge. A constant discharge pressure means constant energy release, which is desirable in certain applications. An even more desired feature would be the amount of the energy being discharged could match with a variable demand. For this enthalpy storage process, pressure energy is a form of energy as important as the temperature energy. A higher output pressure means higher energy flow. A controllable output pressure for the working fluid can bring out the benefit of higher degree of freedom for operation.

To realize discharge pressure control, in one exemplary embodiment, an extra pressure source is provided. In this manner, controlled pressure release of working fluid from working fluid chamber 10 is realized by coupling pressure support chamber 20 with pressure supplementary vessel 210. As explained below, pressure in supplementary pressure vessel 210 is charged either by heating pressure support chamber 20 or by pumping working fluid into working fluid chamber 10 for compressing gas or refrigerant in pressure supplementary vessel 210.

As shown in FIG. 4, a pressure supplementary vessel 210 with a gas chamber 213 and a working fluid chamber 214 is connected to vessel 15 (which is an enthalpy storage vessel). P_(v1) is discharge pressure depending on its opening; P₁ is pressure in enthalpy storage vessel 205; P_(v2) is the controllable valve pressure, which determines the amount of gas from the pressure supplementary vessel 210 to be released to the gas chamber 212 of vessel 15 to maintain it at a constant P₁. P₂ is pressure in pressure supplementary vessel 210. A high P₂ is obtained by pumping working fluid into the working fluid chamber of pressure supplementary vessel 210 to compress the gas chamber 213, as pumping liquid is more efficient than compressing gas directly. To more efficiently use resources, the same pump for refilling the pressure supplementary vessel 210 could be used; P₂ can also be elevated through heating. During the pressure charge of pressure supplementary vessel 210, the valve connected to vessel 15 is closed. When all the working fluid is released, the working fluid in pressure supplementary vessel 210 can also be drained to the reservoir by opening the valve to reduce the pressure level in the system to refill the working fluid to vessel 15. Heat exchanger units 60, 225 are also provided.

The heat supply for the downstream application can be specified by the pressure difference ΔP=P₁−P_(v1), which determines how much hot working fluid should be discharged. To meet a variable demand, P_(v1) can be controlled through the valve opening. The purpose of the pressure supplementary vessel 210 is to maintain P₁ at a constant value. Assume the following is a dynamic model for a system that implements a control algorithm:

P ₁ =f(P ₂ ,P _(v2) ,P _(pump) ,q _(h))

where P_(pump) is the pumping energy gain by pumping the working fluid into chamber 214 of pressure supplementary vessel 210, which is a backup option. If the initial P₂ is high enough to maintain P₁ during the heat discharge process, then this extra pressure supply is optional. The same rationale applies to the option of pressure elevation by extra heat input q_(h). Thus, in this dynamical model, P_(v2) is the main control variable, which determines the amount of gas to be released to enthalpy storage vessel 15, and P_(pump), q_(h) are the optional control variables for backup when P₂ drops to a level that cannot maintain a constant P₁.

As explained above, a single vessel with piston connected chambers is related to one exemplary embodiment of the present invention. There could be different variations of such an enthalpy storage system based on the configurations of the piston connected chambers or vessels, i.e., see FIGS. 5 & 6. The pressure support chamber 20 and working fluid chamber 10 can be included in a single vessel 15, or separated into multiple vessels. Such further exemplary embodiments may be based on suitable sizing requirements for applications and also based on considerations of efficiency, the reliability and lifetime of the equipment under changing pressure and temperature cycling operations.

There are many other thermal energy storage technologies, such as sensible heat storage (hot rock or concrete, molten salt), latent heat storage (solid-to-liquid) and thermochemical heat storage. The most successful application is sensible heat storages. However, it suffers from low energy density. The liquid-to-solid phase change material (PCM) based latent heat storage suffers more challenges, such as low PCM conductivity, material deterioration under long term usage and potential equipment structure damage caused by density change during repeated cycles. To overcome those challenges, the cost of such a system usually is not low. A thermochemical heat storage system is still under research stage, which is more complicated and could be more expensive.

Compared to those common approaches, the present invention has several advantages. First, the storage system is simple and could be cost competitive. Second, due to discharging working fluid will be in a flow condition, a substantially high heat transfer coefficient can be obtained. Thus, this process is cost competitive and suitable for many applications.

By employing different working fluids and refrigerants, it may be possible to cover wide temperature and pressure ranges for different applications. Another advantage of this enthalpy storage process is that it can be used to transform heat to work. A further feature of this process is that it can be configured for large scale applications, as the CAES system is an example, which is usually for large scale applications.

Based on the selections of the working fluid and the refrigerant or the chemical substance, various exemplary embodiments of the present invention can have various applications as described below.

In one exemplary embodiment of the present invention, heat storage is used to produce steam for space heating. For this application, pressure support chamber 20 without a heating unit is used for illustration purposes as shown in FIG. 7A. For example, elastic container 37 (such as a balloon) may be used for pressure elevation support. For the application of heat storage for a community or district buildings, parallel arrangement of vessel units with suitable size could be employed. In domestic space heating, no high pressure is required. Thus, the cost of pumping the cold water back into the working fluid chamber will be small. Refrigerant could also be used for potentially pumping cost reduction. A simpler system may be implemented with a smaller investment.

FIG. 7B illustrates how the optional features illustrated in FIGS. 4 and/or 7A can be combined with some of the other features described above. Mixer 91 enables fluid from working fluid reservoir 35 to be combined with overheated vapor from within vapor conduit 90. The saturated vapor can then be provide to utilization units 18. Also, pressure supplementary vessel 210 may be used to provide additional pressure to pressure support chamber 20. Cooled liquid may flow in either direction between working fluid reservoir 35 and working fluid chamber 214.

Under higher pressure, hot water can be stored at a temperature that is much higher than 100° C., thus resulting in a higher energy density. When hot water is released from the pressurized working fluid chamber 10 and into vapor conduit 90, it turns into overheated steam under a lower environment pressure. For domestic space heating, saturated steam around 100° C. under atmosphere pressure is sufficient. Thus, a stream of cold water from reservoir 35 can be drawn and mixed with the overheated vapor from vapor conduit 90 in mixer 91 to produce more steam for heating purpose. An exemplary structure with multiple sieves (like a distillation column) is illustrated in FIG. 8 in order to mix overheated vapor with liquid working fluid from reservoir 35 to produce saturated vapor. Overheated vapor goes through the sieves 330 and evaporates liquid on the sieves to produce more steam for space heating. The multiple sieves and overflow pipes 320 are desirably to obtain complete evaporation of the inlet cold liquid and robust operation of the mixing. To prevent vapor entering the overflow pipes, the pipes are extended to almost touch the next lower sieve. There are desirably no open holes on the sieves directed to the pipe inlet. In case of accumulation of liquid at the bottom of the mixer, a level controlled discharge valve is located at the bottom. The mixer 91 desirably includes a specific design to produce the saturated steam in a high efficiency way according to application load. With higher temperature water stored in chamber 10, more cold water in the reservoir can be drawn for mixing to produce saturated steam.

TABLE 1 Parameters used for a simplified case estimation L₀ Total length of the pressure vessel L₁ Length of the gas chamber after fully charged R Radius of the pressure vessel P_(mean) Mean average pressure of the overheated vapor being discharged T_(ov) Overheated vapor temperature T_(s) Saturated steam temperature

TABLE 2 Values to be used for the parameters in Table 1 L₀ L₁ R P_(mean) T_(ov) T_(s) 4 m 2 m 1 m 3 Mpa 233.85° C. 100° C.

To estimate the size feasibility of a pressurized vessel as depicted in FIG. 7A for an enthalpy storage process, a simplified case calculation is carried out. The dimensions of a pressure vessel and its average discharge pressure and overheated vapor temperate are listed in Table 2. Thus the total sensible heat J in the vessel is:

J=mC _(p)(T _(mean) −T _(s))=905.9994 kWh/vessel,

where m is the total water mass in the vessel and C_(p) is its heat capacity. FIG. 9 shows the annual heat energy consumption per unit floor area with different insulation levels. For a modern house with 300 m² floor area, and a heating period of 5 months, the total heat energy need Q_(h) is:

$Q_{h} = {\frac{300 \times 150}{5 \times 30} = {300\frac{kWh}{day}}}$

Then:

$\frac{J}{Q_{h}} \approx {3\frac{{houses}\left( {300\mspace{14mu} m^{2}} \right)}{{day} \cdot {vessel}}}$

Thus a vessel with values of the dimensions and parameters listed in Table 2 can provide heating steam for 3 modern houses with 300 m² floor area each for 24 hours. So it can be concluded that the dimensions and pressure and temperature levels of the enthalpy storage process as shown in FIG. 7A are promising for spacing heating applications.

Fast ramping for power generation is desirable due to the increased share of renewable power sources mingling into the grid. The enthalpy storage system can store high pressure and high temperature liquid water and be used to provide instant steam supply to increase the power supply for sudden excessive demand in the grid. When excessive electricity is being generated, hot steam can be drawn and used to charge the pressurized vessel, or electric heaters. The heating source can also come from solar thermal energy. FIG. 10 illustrates how power generation can be backed up with a simplified enthalpy storage vessel, which can be connected to different turbine stages 402 under different working pressures. In the figure, a simple vessel is for illustration. Generator 404, condenser 406 and cooling tower 408 are shown. For a commercial application, multiple vessels could be employed for scale requirement. For the ramping service, if delicate pressure control strategy is needed, then the approach shown in FIG. 6 can be employed.

Many industrial processes require hot steam supply, desirable for intermittent heat sources. Thus the enthalpy storage process could be used to store water at a required high temperature and to provide hot steam for the industrial processes when needed.

In one exemplary embodiment of the present invention, the enthalpy storage process could be used in a concentrated solar power (CSP) plant for energy storage, to provide hot steam to generate electricity when the sun is not shining. Experience and technologies could be borrowed from a CASE system, which is usually for large scale applications, to support the configuration of the current enthalpy storage system. In this manner it is possible to store large amounts of water under high temperature and high pressure—to generate steam for power generation. Because the storage medium is the working fluid itself, the cost of this process could be lower than the use of current molten salt storage technology for a CSP plant.

Whereas many alterations and modifications of the disclosure will no doubt become apparent to a person of ordinary skill in the art after having read the foregoing description, it is to be understood that any particular implementation shown and described by way of illustration is in no way intended to be considered limiting. Therefore, references to details of various implementations are not intended to limit the scope of the claims, which in themselves recite only those features regarded as the disclosure. 

1. Apparatus for heat storage, comprising: a working fluid chamber for storing working fluid; a pressure support chamber coupled to the working fluid chamber and including pressure support material, said pressure support chamber for increasing pressure in said working fluid chamber responsive to compression of said pressure support chamber; a fluid pump for pumping working fluid into the working fluid chamber, wherein pumping fluid into the working fluid chamber increases pressure of said working fluid in the working fluid chamber; said the pressure elevation of the working fluid in the fluid chamber is responsive to pumping the fluid back into the fluid chamber to compress the pressure support chamber; a working fluid chamber heat exchanger for varying temperature in said working fluid chamber; an output conduit for transferring working fluid from said fluid chamber to a utilization destination; an input conduit for transferring said working fluid received from said utilization destination to said working fluid into the fluid chamber.
 2. Apparatus for heat storage according to claim 1, a pressure support chamber heat exchanger for varying temperature of said pressure support material in said pressure chamber;
 3. Apparatus for heat storage according to claim 1, said working fluid received from said utilization destination cools said pressure support material in said pressure support chamber via said pressure support chamber heat exchanger, wherein said pressure in said working fluid chamber decreases responsive to said pressure support material in said pressure support chamber being cooled;
 4. Apparatus for heat storage according to claim 1, wherein a further cooling source cools said pressure support material in said pressure support chamber.
 5. Apparatus for heat storage according to claim 1, wherein said pressure support chamber heat exchanger is also for increasing pressure in said pressure support chamber through heating the pressure support material.
 6. Apparatus for heat storage according to claim 1, wherein said pressure support material is selected from the group consisting of gas, refrigerant, and chemical substance.
 7. Apparatus for heat storage according to claim 1, wherein said when the pressure support material is either a refrigerant or a chemical substance, heating is to increase the pressure in the pressure support chamber through phase change to elevate the working fluid pressure stored in the fluid chamber and cooling is to reduce the pressure in the pressure support chamber through phase change to reduce or even eliminate pumping energy to refill the working fluid to the fluid chamber.
 8. Apparatus for heat storage according to claim 1, wherein said pressure support chamber forms a pressure support chamber void that is encapsulated with elastic material.
 9. Apparatus for heat storage according to claim 1, wherein said input conduit includes a fluid reservoir situated between said utilization destination and said working fluid chamber.
 10. Apparatus for heat storage according to claim 1, wherein said working fluid chamber and said pressure support chamber are included in a common container that includes a piston that seals and separates said working fluid chamber and said pressure support chamber by forming a barrier there between.
 11. Apparatus for heat storage according to claim 1, wherein said working fluid chamber and said pressure support chamber are located in respectively different containers with a piston apparatus therebetween, so that pressure in said working fluid chamber changes responsive to volumetric change of said pressure support chamber.
 12. Apparatus for heat storage according to claim 1, said controlled pressure release of the working fluid from the working fluid chamber is realized by coupling the pressure support chamber for the main energy storage container with an extra pressure supplementary vessel at higher pressure; said the pressure in the supplementary pressure vessel is charged either by heating the pressure support chamber or through pumping the working fluid into a working fluid chamber for compressing the gas or refrigerant in the pressure support chamber of the pressure supplementary vessel.
 13. Apparatus according to claim 1, said apparatus including at least one controller for performing the steps of: Heating the pressure support material via the pressure support chamber heat exchanger to transition the pressure support material from liquid to gas and increase the pressure in the pressure support chamber; Opening a valve to allow the working fluid to exit the working fluid chamber and interact with the utilization destination; Allowing the working fluid to cool the pressure support material after interacting with the utilization destination; and Refilling the working fluid into the working fluid chamber after interacting with the utilization destination.
 14. Apparatus for heat storage according to claim 1, said a mixer with multiple sieves with overflow pipes on each of them is employed to mix overheated vapor with liquid working fluid from the reservoir to produce saturated vapor.
 15. Apparatus according to claim 1, wherein the pressure support chamber and the working fluid chamber are insulated.
 16. A method of heat storage, said method comprising the steps of: storing working fluid in a working fluid chamber; compressing a pressure support chamber that is coupled to the working fluid chamber and that includes pressure support material, wherein responsive to compression of the said pressure support chamber, pressure in said working fluid chamber is increased; pumping working fluid into the working fluid chamber, wherein pumping fluid into the working fluid chamber increases pressure of said working fluid in the working fluid chamber; wherein pressure elevation of the working fluid in the fluid chamber is responsive to pumping the fluid back into the fluid chamber to compress the pressure support chamber; varying temperature in said working fluid chamber; transferring working fluid from said fluid chamber to a utilization destination; and transferring said working fluid received from said utilization destination to said working fluid into the fluid chamber.
 17. A method according to claim 16, further comprising varying temperature of said pressure support material in said pressure chamber via a heat exchanger.
 18. A method according to claim 16, said working fluid received from said utilization destination cools said pressure support material in said pressure support chamber via said pressure support chamber heat exchanger, wherein said pressure in said working fluid chamber decreases responsive to said pressure support material in said pressure support chamber being cooled;
 19. Method according to claim 16, wherein a further cooling source cools said pressure support material in said pressure support chamber.
 20. A method according to claim 16, wherein said pressure support material is selected from the group consisting of gas, refrigerant, and chemical substance.
 21. A method according to claim 16, wherein said when the pressure support material is either a refrigerant or a chemical substance, heating is to increase the pressure in the pressure support chamber through phase change to elevate the working fluid pressure stored in the fluid chamber and cooling is to reduce the pressure in the pressure support chamber through phase change to reduce or even eliminate pumping energy to refill the working fluid to the fluid chamber.
 22. Apparatus for heat storage according to claim 1, wherein said input conduit includes a fluid reservoir situated between said utilization destination and said working fluid chamber.
 23. A method according to claim 16, wherein controlled pressure release of the working fluid from the working fluid chamber is realized by coupling the pressure support chamber for the main energy storage container with an extra pressure supplementary vessel at higher pressure; said the pressure in the supplementary pressure vessel is charged either by heating the pressure support chamber or through pumping the working fluid into a working fluid chamber for compressing the gas or refrigerant in the pressure support chamber of the pressure supplementary vessel.
 24. A method according to claim 16, said method further comprising the steps of: Heating the pressure support material via the pressure support chamber heat exchanger to transition the pressure support material from liquid to gas and increase the pressure in the pressure support chamber; Opening a valve to allow the working fluid to exit the working fluid chamber and interact with the utilization destination; Allowing the working fluid to cool the pressure support material after interacting with the utilization destination; and Refilling the working fluid into the working fluid chamber after interacting with the utilization destination. 